Network test instrument with cable connection and signature testing

ABSTRACT

A test instrument can be coupled to a test point and measure signals in the network. The test instrument may determine whether the test instrument is connected to a cable of the network and provide notification if the test instrument is not connected to a cable. The test instrument may also detect when it is connected to a customer premises that has been previously been tested through reflected signal signatures.

PRIORITY

This application is a Continuation of commonly assigned and co-pendingU.S. application Ser. No. 14/836,770 filed Aug. 26, 2015, the disclosureof which are hereby incorporated by reference in their entireties.

BACKGROUND

Service provider networks typically delivers services, such as digitaltelevision, high-speed Internet, Voice-over-IP (VoIP), etc., to customerpremises. Also, the networks typically carry bi-directional traffic. Forexample, a typical cable network is a two-way hybrid fiber-coaxial (HFC)network that supports point-to-multipoint transmission in the downstreamdirection using digital signals or a mix of analog and digital signals,and multipoint-to-point transmission in the upstream direction.Downstream signals, which carry broadcast digital TV signals, Internettraffic, etc., are distributed via a fiber optic connection from ahead-end to a node that converts the optical signals to electricalsignals and then distributes the signals to customer premises via a treeand branch coaxial cable distribution network termed ‘cable plant’.Recently, service providers are running fiber to the customer premisesto improve bandwidth. At the customer premises, terminal equipmentsupports the delivery of services, which may include video, data andvoice services, to customers for example via cable modems. Upstreamsignals from the customer premises may carry phone and Internet traffic.The upstream signals propagate from the branches of the cable planttowards the headend of the network.

The upstream and downstream signals are prone to impairments originatingat various locations in the network. There may be numerous devices,cable segments and connectors located between the fiber optic node andthe customer premises equipment where defects can occur, and defects andimpairments can occur at different customer premises that can impact thesignal quality of other customer premises. Tracing a source of animpairment typically requires that a technician travels to differentnetwork locations and takes measurements to locate the sources of theimpairments, and generally, throughout the day, technicians may travelto multiple locations to measure, diagnose and correct impairments.Portable network testing devices currently used in the industry may helpto identify certain types of defects by performing various measurements,such as spectral and noise measurements.

BRIEF DESCRIPTION OF DRAWINGS

Features of the present disclosure are illustrated by way of examplesshown in the following figures. In the following figures, like numeralsindicate like elements, in which:

FIG. 1 illustrates a network with a test instrument connected at a testpoint, according to an example of the present disclosure;

FIGS. 2A-B illustrates multiple test points, according to examples ofthe present disclosure;

FIGS. 3A-B illustrate a single port and a dual port test instrument,according to examples of the present disclosure;

FIG. 4 illustrates circuit components of a test instrument, according toan example of the present disclosure;

FIGS. 5-6 illustrate methods, according to examples of the presentdisclosure;

FIGS. 7A-D show signatures, according to examples of the presentdisclosure; and

FIGS. 8A-B show information that may be displayed on a test instrument,according to examples of the present disclosure.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring mainly to examples thereof. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present disclosure. It will be readilyapparent however, that the present disclosure may be practiced withoutlimitation to these specific details. In other instances, some methodsand structures have not been described in detail so as not tounnecessarily obscure the present disclosure. Throughout the presentdisclosure, the terms “a” and “an” are intended to denote at least oneof a particular element. As used herein, the term “includes” meansincludes but not limited to, the term “including” means including butnot limited to. The term “based on” means based at least in part on.

A test instrument for networks may be connected to a network to measureparameters or characteristics of signals transmitted in the network. Atest instrument for example is an apparatus that can connect to a cable,for example via a port, and can determine information about signalstransmitted on the cable. The cable may be connected to or be part of asystem, e.g., a network, and the test instrument can determineinformation about signals transmitted in the network via the cable. Thetest instrument may be a handheld portable device or a larger device.The test instrument may include a single port or multiple ports toconnect to a single cable of the network or to multiple cables of thenetwork simultaneously to take measurements.

Some examples of signal measurements performed by the test instrumentmay include spectral and noise measurements. The test instrument may useFrequency-Domain Reflectometry (FDR) and/or Time-Domain Reflectometry(TDR) to measure reflections, i.e., reflected signals. Reflectometrypulses (e.g., TDR or FDR pulses) may be generated and output via a portof the test instrument, and characteristics of the reflected signals,such as amplitude and reflection time, i.e., the time it takes for thepulse to return to the port, are measured to determine signalsignatures, detect locations of impairments, etc. Signal levels aremeasured and displayed for example to verify proper levels arriving atthe test point. Frequency response is measured for example to verifyproper losses and to uncover any roll-off or sharp changes in response.

According to examples of the present disclosure, the test instrument maydetermine whether its port is connected to a cable of a predeterminedminimum length prior to taking signal measurements. For example, using ameasurement technique such as FDR or TDR, the test instrument determineswhether it is connected to an external wire, and may display anotification that it is improperly connected to wiring if the testinstrument determines that it is not connected to a minimum lengthcable. Cable connection testing may be used to verify a cable isproperly connected before testing. The test instrument may determine TDRand/or FDR signatures comprised of measured characteristics of reflectedsignals. A unique signature may be determined for each test location,such as a signature for each customer premises. The measuredcharacteristics may include amplitude (e.g., signal level in decibels),reflection time, peak detection at identified times, etc. From thesignatures, the test instrument can determine whether it is connected todifferent customer premises than previously connected and to compare thesignature to stored signatures to determine whether the test instrumentis connected at a desired location. Notifications may be displayedregarding the signature determinations. Notifications may also bedisplayed identifying and notifying if there are unexpected reflectionson a section of wiring.

The cable connection testing may be used to insure that measurements arebeing taken from a properly connected cable. Also, the signature testingmay be used to determine whether measurements are being taken at desiredlocations that have predetermined signatures. For example, techniciansmay be required to take many measurements per day and this testingensures that the technicians are actually taking the measurements ratherthan faking measurements. For example, if a measurement is taken whenthe test instrument is not connected to a cable, the measurements mayindicate a flat signal that can be construed as a proper signal, or atechnician may mock-up a piece of cable with an impedance connected onone end, such as a splitter, and connect the other end to the testinstrument to fake measurements at different locations. The cableconnection testing ensures a cable of proper length is connected to thetest instrument for taking signal measurements, and the signaturecomparison can determine that the test instrument is not connected tothe same cable for every measurement and can also be used to determinethat the measurements are being taken at desired locations.

The test instrument may include a processor, display, and data storageto store and display measurements and notifications, and to storesignatures and other information. The test instrument may include anetwork interface, such as WiFi, Bluetooth, Ethernet, cellular, etc., toconnect the test instrument to other devices via a network, and totransmit the stored data to other devices or computers. In one example,the test instrument is a portable, hand-held device that may connect tothe cloud or any remote computer via the network interface. In otherexamples, the test instrument may be part of a larger system. The testinstrument may be used to measure signals in any suitable type network,include cable television networks, optical networks, in-home wiring,etc.

FIG. 1 illustrates a test instrument 100 connected to a network 101according to an example of the present disclosure. In this example, thenetwork 101 is a cable TV network but the test instrument 100 may beused in other types of networks. Network 101 shown in FIG. 1 may be alocal portion of a hybrid fiber coaxial (HFC) network that deliversCable Television (CATV) signals, including digital TV signals and dataand control signals, to end users at customer premises 53.

A fiber-optic node 10 of the cable network 101 for example includes adownstream (DS) optoelectronic converter 10A that converts downstream(DS) optical signals generated by a remote Cable Modem TerminationSystem (CMTS) (not shown) into downstream electrical RF signals 11, andan upstream (US) electro-optic converter 10B that converts upstream (US)electrical RF signals 13 into US optical signals for upstreamtransmission to the remote CMTS. The fiber-optic node 10 is coupled viaa coaxial cable 12 to a bidirectional amplifier 15, which amplifies thedownstream RF signals 11 for distribution to first and second groups ofcustomer premises 53A and 50B. The downstream RF signals 11 generated bythe downstream optoelectronic converter 10A of the fiber node 10 aredistributed to a plurality of end-of-the-line subscribers, or end usersfor example via one or more trunk coaxial cables 44 and subscriber taps51. At the customer premises 53, the DS signals are demodulated usingcable modems (not shown). One or more two-way trunk RF amplifiers 40 mayfurther be provided in each trunk cable 44 to suitably amplify theupstream and downstream CATV signals on their way to and from thecustomer premises 53. The first and second groups of customer premises50A and 50B may send upstream signals 31A and 31B, respectively, whichmay be combined by the bidirectional amplifier 110 into the upstream RFsignal 13 propagating towards the fiber node 106 for delivering to theremote CMTS at the headend (not shown). The cable network 101 may servea large number of customer premises, which may be connected by taps 51to a plurality of different cable trunks 44 at a plurality of differentlocations. The trunk cables 44 may be buried in the ground or they maybe elevated above the ground on utility poles, or a combination of both.In other examples, fiber cables may be run to the home and the testinstrument 100 may connect to the fiber cables.

The test instrument 100 may be connected to the cable network 101 at adesired test point to test signals (upstream and/or downstream) passingthrough the test point. The test instrument 100 is shown as connected attest point 105. The test instrument 100 may be connected at any locationwhere connections are available to connect to the network 101. Forexample, the test instrument 100 is connected to the network 101 via atest access point (tap) to measure signals flowing through the tap. Thetap for example is a 3 port hardware device and one port is monitor portconnectable to the test instrument 100 to measure signals in the networkpassing through the tap. The tap may provide more than test pointaccess. For example, the tap may be a hardware device that ‘taps” offthe line and feeds one or more customer premises and is where the testinstrument 100 can be connected.

The test instrument 100 may include one or more ports to connect to thetest point 105. In an example, the port(s) include coaxial RF cableconnectors. It will be appreciated that test instrument 100 may alsohave other non-cable ports, for example to connect to a computer or toan external display, such as but not exclusively one or more USB portsand the like.

The test instrument 100 is inserted by coupling a port of the testinstrument 100 to a cable in the network 101. In this manner, signals inthe network are received at the test instrument 100. The test instrument100 for example may include a dual port test instrument. For example,one port may be connected downstream such as toward a customer premises,and one port may be connected upstream towards a network node. Signals(e.g., upstream or downstream) in the network may flow through the testinstrument 100 and may be measured. In another example, the testinstrument 100 may be a single port device. For example, the testinstrument 100 is connected to the network via a test access point (tap)to measure signals flowing through the tap at the test point 105. Thetap for example is a 3 port hardware device and one port is monitor portconnectable to the test instrument 100 to measure signals in the networkpassing through the tap. A dual port test instrument may also beconnected to a tap.

FIGS. 2A-B show examples of connecting the test instrument 100 atdifferent segments of the network 101. FIG. 2A shows the test instrument100 connected to a tap 250 a in a portion of the network 101 betweenamplifier 40 a and customer premises 53 a. There may be multiple taps250 a-n and the values (e.g., 26, 23, 20 . . . ) shown for the taps 250a-n are examples of tap values, e.g., attenuation measured at the tap,in decibels. The downstream signal is significantly attenuated by thetime it reaches the endpoint, which may be a customer premises. Acustomer premises may also be connected via a drop line 220, alsoreferred to as a trunk line, at each tap. The test instrument 100 inthis example is dual port device with ports 1 and 2. Port 1 is connectedvia a jumper cable 221, e.g., 4-6 feet coaxial cable, to the tap 250 a.Port 2 is connected to network interface unit (NIU) 210 of customerpremises 53 a. The NIU 210, also referred to as a network interfacedevice, typically is attached to the outside of the customer premisesand is where the drop line connects to the in-home orin-customer-premises wiring. The NIU 210 is typically connected to aground block. The splitter 211 may be in the customer premises 53 a andis an impedance that reflects a reflectometry pulse output from the testinstrument 100 as is further described below.

Connecting the test instrument 100 as shown in FIG. 2A can be used totest wiring and signals at the tap 250 a, which may be at a node ortelephone pole. For example, a reflectometry pulse is output at port 2from the test instrument 100 to determine whether there is anyimpairments, such as broken cable, in the drop line 220. Prior to takingmeasurements to detect the impairments, the test instrument 100determines whether port 2 is connected to a cable of a predeterminedminimum length and also determines if the signature of a reflectedsignal received at port 2 is different than a previous signature and/orspecific to the location of the test point for example to help ensurethat port 2 is properly connected to the drop line 220 for the desiredcustomer premises. Test instrument 100 may be a single port device. Forexample, the single port may be connected to the drop line 220 tomeasure signals on the drop line 220.

FIG. 2B also shows the test instrument 100 connected at a different testpoint, such as between the NIU 210 and the splitter 211. From this testpoint, the test instrument 100 may take measurements to identifyimpairments at the customer premises 53 a. Similarly to FIG. 2A, priorto taking measurements to detect the impairments, the test instrument100 determines whether port 2 is connected to a cable of a predeterminedminimum length, such as the cable 222 connected to splitter 211 and mayalso determine if the signature of a reflected signal received at port 2is different than a previous signature and/or specific to the currentlocation or customer premises.

FIGS. 3A-B show examples of components of the test instrument 100,according to an example. FIG. 3A shows an example of the test instrument100 as a single port device with only port 121 to connect to network 101to measure signals in the network 101, and FIG. 3B shows an example ofthe test instrument 100 as a dual port device with ports 121 and 122 toconnect to the network 101 to measure signals. As shown in FIG. 3A, asignal processing circuit 130, which may be connected to the port 121,is configured for processing signals from the network 101 that arereceived via the port 121 to obtain measurement data 139. A pulsegenerator 131 (e.g., TDR or FDR) generates reflectometry pulses whichare output via port 121 and are reflected back to the port 121 fromimpedances in the network 101. The reflected pulses, also referred to asreflected signals, are measured by the signal processing circuit 130 togenerate the measurement data 139 and determine a signature from themeasurement data. A control processor 150 may be communicatively coupledto the signal processing circuit 130 and is configured to process themeasurement data 139 and make the determinations described herein, suchas whether the port 121 is connected to a minimum length cable,determine a signature of the signal, determine whether the signature isunique to the test point or whether the signature is the same as aprevious signature, testing wire integrity, etc. The processor 150 maydisplay measurements and notifications on display 160. A keypad 161,touch screen or another I/O device may be provided to receive userinput. Interface 162 may include one or more interfaces, such as USB,Bluetooth, WiFi, etc. The signal processing circuit 130 and processor150 may be embodied using a single dedicated or shared hardwareprocessor or using multiple hardware processors, and/or a combination ofsoftware and hardware. Examples of hardware processors that may be usedto implement the components including a digital signal processor (DSP),application specific integrated circuit (ASIC), field programmable gatearray (FPGA), network processor, system on a chip, microprocessor,Complex Programmable Logic Device (CPLD), erasable programmable logicdevice (EPLD), simple programmable logic device (SPLD), or macrocellarray. Data storage 151 may store measurement data, signatures or anyinformation used by the test instrument 100. In an example, one or moreof the functions and steps of the methods may be performed by theprocessor 150 or other hardware executing machine readable instructionsstored in a non-transitory computer readable medium, such as the datastorage 151. The data storage may comprise RAM (random access memory),ROM (read only memory), EPROM (erasable, programmable ROM), EEPROM(electrically erasable, programmable ROM), hard drives, flash memory, orother types of storage devices, which may be volatile and/ornonvolatile.

FIG. 3B is similar to FIG. 3A but includes additional port 122connectable to the network 101 and signal processing circuit 140 forprocessing signals from the network 101 that are received via the port122 to obtain measurement data 149. Processor 150 process themeasurement data 149 to make determinations described herein. The ports121 and 122 allow the test instrument 100 to connect simultaneously toan upstream portion of the network 101 and to a downstream portion ofthe network 101. In an example, the port 121 receives downstream signalsand the port 122 receives upstream signals, and measurement data 139 isdownstream measurement data and measurement data 149 is upstreammeasurement data.

FIG. 4 shows additional details of the components of the test instrument100 shown in FIG. 3A for the single port example. Although not shown,similar components may be provided for the dual port example shown inFIG. 3B. FIG. 4 shows pulse generator 131, which may be a TDR or FDRreflectometer. The pulse generator 131 may be coupled to the signalprocessing circuit 130 and the port 121. The pulse generator 131 injectsa probe signal (e.g., reflectometry pulse 146) into the network 101through a coupler or switch 142 and port 121. The measurement processor147 may include reflectometer control logic for controlling theoperation of pulse generator 131 and processing measurement results.

The signal processing circuit 130 may include an optional gain controlunit 141 that is operationally followed by an Analog to DigitalConverter (ADC) 143, a Digital Downconverter/Fast Fourier Transform(DDC/FFT) unit 145, and measurement processor 147. The DDC/FFT logic 145may be configured to obtain a frequency spectrum of signal 170 (e.g.,reflected signal) within the frequency band of transmission, for exampleby performing the FFT of 170, and/or to tune to an active channel usingdigital down-conversion. The active channel to tune to may be selected,for example, by a user command or automatically by internal testerprogramming, and communicated to the DDC/FFT logic 145 by the controlprocessor 150 and/or the measurement processor 147.

The measurement processor 147 may be configured to obtain measurementdata 139 related to signal 170, including diagnostic information, fromthe output of the DDC/FFT unit 145 and optionally by querying the ADC143 and/or the gain control unit 141. The measurement data 139 mayinclude frequency of each channel detected in the signal 170, and mayalso include channel diagnostic information for one or more of thedetected or active channels. The channel diagnostic information mayinclude at least one of the following channel parameters orcharacteristic: signal level of the detected downstream channel, amodulation type of the detected downstream channel, signal-to-noise(SNR) for the channel, bit error ratio (BER) for the detected channel,modulation error ratio (MER) for the detected channel, ingress under thecarrier, in Channel Frequency Response (ICFR), adaptive equalizationcoefficients, Digital Quality Index (DQI), etc. To this end, themeasurement processor 147 may include (not shown) a frequency scan logicfor controlling the DDC/FFT unit 145 and obtaining active channel datatherefrom, and a QAM demodulator for demodulating the selected channel;the QAM demodulator may include an adaptive equalizer, and measurementcontrol logic (MCL) to determine various performance-related data andperform a variety of service level tests and to obtain the channeldiagnostic information.

FIG. 5 illustrates a method 500 for determining whether a testinstrument is connected to a minimum length cable. The method 500 andother methods described herein are described by way of example as beingperformed by the test instrument 100 shown in FIGS. 1-4, but the methodsmay be performed by other test instruments. Also, one or more steps maybe performed in different orders or substantially simultaneously. At501, a reflectometry pulse, such as a TDR or FDR pulse, is output fromthe test instrument onto a cable connected to or in the network 101. Forexample, the pulse generator 131 generates the pulse and it is outputvia one or more ports (e.g., 121 and/or 122) of the test instrument 100.The amplitude and frequency of the pulse may be adjusted or selected asneeded. Short pulses may be used to test short cables and longer pulseswith higher signal strength may be used to test longer cables. The pulsegenerator 131 may output multiple reflectometry pulses.

At 502, a reflected signal or signals are received (e.g., signal 170)for example via port 121. For example, the reflectometry pulse travelsdown the cable in the network 101 and pulse is reflected by animpedance, such as splitter 211 shown in FIGS. 2A-B, and the reflectedsignals travel back towards the port 121 and are received at the port121.

At 503, characteristics of the reflected signals are measured. Forexample, reflection time is measured, which is the length of time ittakes to receive the reflected signal from the output of thereflectometry pulse. For example, measurement processor 147 invokes thepulse generator 131 to send the reflectometry pulse and starts keepingtrack of the time or notifies the processor 150 that the pulse is sentand the processor 150 keeps track of the time. The measurement processor147 determines when the reflected signal corresponding to thereflectometry pulse is received and the processor 150 is notified of thereceipt of the reflected signal. The time of receipt is determined, andthe length of time between the sending of the reflectometry pulse andthe receiving of the corresponding reflection signal is the reflectiontime. Other characteristics of the reflected signal may also bemeasured, including signal strength, as discussed above.

At 504, the processor 150 determines whether the test instrument isconnected to a minimum length cable based on at least one of themeasured characteristics of the reflected signal. The minimum lengthcable for example is a cable of predetermined length. For example, aminimum length may be 6 inches or one foot or any length, such as anylength that is indicative measurements are being taken from signalsreceived via a connected cable rather than from no connected cable. Inan example, measured reflection time is used to determine length of aconnected cable. For example, cable speed is determined and may be apreset value stored in the data storage 151. From the cable speed andreflection time, distance is determined. The distance is assumed to bethe cable length of a connected cable. If the determined cable length isgreater than or equal to the length of the minimum length cable, thenthe processor 150 determines that the test instrument 100 is connectedto a cable of at least the minimum length. Then, at 505, othermeasurements and operations are performed and a notification may bedisplayed that the cable is connected. If the determined cable length isless than the length of the minimum length cable, then the processor 150determines that the test instrument 100 is not connected to a cable ofat least the minimum length. At 506, the processor 150 may generate anotification that a cable is not connected and may not allowmeasurements or further processing until the cable is connected. FIG. 8Ashows an example of information that may be displayed on the display 160to indicate that a cable is not connected. The user may choose to ignorethe notification or configure or retry after connecting again.Notifications may also be in the form of messages transmitted frominterface 162 to other computers or devices. In addition to reflectiontime, other measured signal characteristics may be considered, such asamplitude (signal strength).

FIG. 6 illustrates a method 600 for comparing signatures of reflectedsignal, which may be performed to determine whether the test instrument100 is capturing signals at a location or customer premises that isdifferent from a previous one, and to determine whether the testinstrument 100 is connected at a desired location. At 601 a signature isdetermined for a reflected signal. For example, after step 505 of themethod 500, the signature is determined of the reflected signal. Thesignature may include amplitude (e.g., signal level in decibels),reflection time, peak detection at identified times, and/or othermeasured characteristics. Signatures may be determined by themeasurement processor 147 and/or processor 150 and examples ofsignatures are shown in FIGS. 7C-D.

At 602, the processor 150 compares the signature determined at 601 witha stored signature. For example, signatures are stored in the datastorage 151 for different test points. The stored signatures may beassociated with different test points, customer premises and geographiclocations. The stored signatures may be signatures previously capturedby the test instrument 100 at other test points. Also, signatures may beloaded into the test instrument 100 for example via interface 162.

At 603, the processor 150 determines whether the test instrument 100 isconnected at an incorrect location or customer premises or is notconnected to a different location or customer premises from which it waspreviously connected based on the comparison at 602. For example, asignature is determined for a customer premises. The signature is storedin the data storage 151. A signature is subsequently determined when thetest instrument 100 is supposed to be connected at another location tomeasure signals for a second customer premises. The processor 150compares the signatures. If the signatures are the same, the processor150 determines that the test instrument 100 has not connected at thesecond location. For example, either the test instrument 100 is stillconnected at the first location or the technician may have mocked up apiece of cable with an impedance connected on one end to fakemeasurements at different locations. A notification may be displayedthat indicates a non-unique home or signature is detected. FIG. 8B showsan example of information that may be displayed on the display 160 toindicate that the test instrument is detecting a non-unique signature.The user may choose to ignore the notification or configure or retryafter connecting again.

In another example, the test instrument 100 stores signatures formultiple different customer premises. The processor 150 may determinewhether the measured signature matches a stored signature to determinewhether the test instrument 100 is currently connected at the desiredlocation.

FIGS. 7A-D show examples of signatures. These figures show the reflectedsignals for example measured at the ground block, such as shown in FIG.2B, and at the tap, such as shown in FIG. 2A. The graphs may bedisplayed on the test instrument display 160. FIG. 7A shows thesignature of reflected signals when no cable is connected. FIG. 7B showsa signature when the test instrument 100 is connected at the groundblock, such as shown in FIG. 2B, and FIG. 7C shows a signature when thetest instrument 100 is connected at the tap, such as shown in FIG. 2A.Each home or customer premises may have a unique set of reflections suchas indicated in FIG. 7C that represent its signature. FIG. 7D shows thatthe same signature of the home may be recognized from different testpoints (e.g., ground block and tap) connected to the home. Also, fromthe display shown in FIG. 7D, the signatures may be saved to the datastorage 151 and synchronized with remote storage, such as on the cloud.

What has been described and illustrated herein is an example along withsome of its variations. The terms, descriptions and figures used hereinare set forth by way of illustration only and are not meant aslimitations. Many variations are possible within the spirit and scope ofthe subject matter, which is intended to be defined by the followingclaims and their equivalents in which all terms are meant in theirbroadest reasonable sense unless otherwise indicated.

What is claimed is:
 1. A test instrument comprising: an input to receivea reflected pulse, wherein the reflected pulse is a pulse generated by apulse generator that is reflected and received via at least one port ofthe test instrument; a measurement circuit to measure characteristics ofthe reflected pulse received via at least one port, wherein the measuredcharacteristics comprises at least one of amplitude, reflection time, orpeak detection of the reflected pulse; a data storage storing asignature of the reflected pulse for a predetermined test location,wherein the signature is a unique signature associated with thepredetermined test location; and a processing circuit to: determinewhether the at least one port is connected to a minimum length cablebased on the measured characteristics of the reflected pulse, and use asignature comparison technique to determine whether a signaturedetermined from the measured characteristics of the reflected pulsematches the stored signature to determine whether the test instrument isconnected at the predetermined test location, wherein a match betweenthe signature determined from the measured characteristics and thestored signature that is unique to the predetermined location indicatesthat the test instrument is connected at the predetermined test locationassociated with the stored signature.
 2. The test instrument of claim 1,wherein, in response to determining the at least one port is notconnected to a minimum length cable, the processing circuit performingat least one of providing notification that the test instrument is notconnected to a minimum length cable and preventing measurements of thesignals received via the at least one port.
 3. The test instrument ofclaim 1, wherein to determine whether the at least one port of the testinstrument is connected to a minimum length cable, the processingcircuit is to determine a reflection time of the pulse, and determinewhether a minimum length cable is connected to the at least one portbased on the reflection time.
 4. The test instrument of claim 3, whereinthe processing circuit determines whether a minimum length cable isconnected to the at least one port based on the reflection time and asignal transmission velocity of the minimum length cable.
 5. The testinstrument of claim 1, wherein the pulse comprises a time domainreflectometry pulse or a frequency domain reflectometry pulse.
 6. Thetest instrument of claim 1, wherein the measured characteristicscomprises reflection time and amplitude of the reflected pulse.
 7. Thetest instrument of claim 1, wherein the reflected pulse comprises thepulse reflected from an impedance back towards the at least one port. 8.The test instrument of claim 1, wherein the signature is based onamplitude and time of at least one peak in the reflected pulse.
 9. Anon-transitory computer-readable storage medium having an executablestored thereon, which when executed instructs a processor to perform amethod as follows: receive a reflected pulse, wherein the reflectedpulse is a pulse generated by a pulse generator that is reflected andreceived by a port the test instrument; measure characteristics of thereflected pulse received via the port, wherein the measuredcharacteristics comprises at least one of amplitude, reflection time, orpeak detection of the reflected pulse, and wherein the reflected pulseis the pulse reflected from an impedance in a system; store a signatureof a reflected pulse for a predetermined test location, wherein thesignature is a unique signature associated with the predetermined testlocation; determine, by a processing circuit, whether the port isconnected to a minimum length cable based on the measuredcharacteristics of the reflected pulse; and use a signature comparisontechnique to determine whether a signature determined from the measuredcharacteristics of the reflected pulse matches the stored signature todetermine whether the test instrument is connected at the predeterminedtest location, wherein a match between the signature determined from themeasured characteristics and the stored signature that is unique to thepredetermined location indicates that the test instrument is connectedat the predetermined test location associated with the stored signature.10. The non-transitory computer-readable storage medium of claim 9,further comprising: performing, in response to determining the port isnot connected to the minimum length cable, at least one of providingnotification that the test instrument is not connected to the minimumlength cable and preventing measurements of signals received via theport.
 11. The non-transitory computer-readable storage medium of claim10, wherein determining whether the port is connected to a minimumlength cable comprises: determining a reflection time of the pulse; anddetermining whether the minimum length cable is connected to the portbased on the reflection time.
 12. The non-transitory computer-readablestorage medium of claim 11, wherein determining whether the minimumlength cable is connected to port is based on the reflection time and asignal transmission velocity of a predetermined cable.
 13. Thenon-transitory computer-readable storage medium of claim 9, wherein thepulse comprises a time domain reflectometry pulse or a frequency domainreflectometry pulse.
 14. The non-transitory computer-readable storagemedium of claim 9, further comprising: providing notification that thetest instrument is not connected at the predetermined location inresponse to determining the signature and the stored signature do notmatch; and allowing measurement of the signals at the test instrument inresponse to determining the signature and the stored signature match.15. The non-transitory computer-readable storage medium of claim 9,wherein the signature of the reflected pulse is based on amplitude andtime of at least one peak in the reflected pulse.
 16. A methodcomprising: determine whether a port of a test instrument is connectedto a minimum length cable by measuring, using a measurement circuit,characteristics of a reflected pulse received at the port, wherein thereflected pulse is a pulse generated by a pulse generator that isreflected and received via the port, and wherein the measuredcharacteristics comprises at least one of amplitude, reflection time, orpeak detection of the reflected pulse; using a signature comparisontechnique to determine, by a processing circuit, in response todetermining the port is connected to the minimum length cable, whether asignature determined from the measured characteristics of the reflectedpulse matches a stored signature to determine whether the testinstrument is connected at a predetermined test location, where thesignature is a unique signature associated with different test pointsand compared to the stored signature at the same test points; anddetermining, by the processing circuit, whether the test instrument isconnected at these test points based on the comparison of the signatureto the stored signature at the same test points.
 17. The method of claim16, wherein determining whether the minimum length cable is connected toport is based on the reflection time and a signal transmission velocityof a predetermined cable.
 18. The method of claim 16, wherein thereflected pulse comprises a time domain pulse or a frequency domainpulse.
 19. The method of claim 16, further comprising: providingnotification that the test instrument is not connected at thepredetermined location in response to determining the signature and thestored signature do not match; and allowing measurement of the signalsat the test instrument in response to determining the signature and thestored signature match.
 20. The method of claim 16, wherein thesignature of the reflected pulse is based on amplitude and time of atleast one peak in the reflected pulse.